The present invention relates to a method and component for monitoring and controlling access to a device in a network environment.
In the present specification, machines to which devices are connected are referred to as device machines and machines requesting access to devices are known as client machines. For clarity the machines are shown separately, but it will be seen that when employing a multi-processing operating system like Windows NT from Microsoft Corporation, device and client software may in fact be running on the same computer and so logically the same computer may be acting as both a client and a device machine.
Referring now to FIG. 1, in a networked environment the attachment of client machines 10 to devices 12 across a network 22 needs to be managed. It is usual in such an environment for client machines to include an arbitrator 14 and for device machines 20 to include a server component 16 which determines which client machine is to obtain access to a device 12. Where a process 17-19 in the client machine needs exclusive access to a device, its arbitrator 14 causes the server component 16 to lock the device thus excluding other client machines from accessing the device.
The client arbitrator 14 in these excluded machines usually keeps retrying to access the device for a predetermined period before replying to a calling client process with a time out message. Once any calling client processes 17-19 in the original client machine are finished with a device, the associated client arbitrator 14 instructs the server component 16 in the device machine to release the lock on the device, thus allowing other client machines access.
It is known for server components to periodically check if a client machine who has locked a device is still operational or to be notified if a client machine terminates abnormally. A problem exists, however, in that the device machine cannot know the current status of client processes unless a high burden of monitoring these processes is placed on the device machine. It is therefore possible for a client process which has requested the client arbitrator to access and lock a device to terminate abnormally but for the client machine to continue to operate. In such a case, the device machine may never know that the client machine should have released the lock giving access to the device and so the device may continue to be locked for longer than necessary.
It is not acceptable in environments such as banking to require a client machine to be turned off simply because a single process has terminated abnormally, particularly if such a machine also acts as a device machine which could be servicing other clients.
Solutions to this problem are that the device machine simply disconnects the client machine if the client has had access to a device for more than a pre-determined period of time or if no activity has taken place for more than a pre-determined period. These are less than satisfactory solutions as the device remains locked for longer than necessary and the abrupt disconnection of the client may indeed be a reason for less than robust client processes failing.
It is therefore an object of the present invention to provide a method and component operable within such a network for mitigating the above problems.
Accordingly, the present invention provides as client arbitrator operable in a multi-processing operating system for monitoring and controlling a client machine""s access to one or more devices, said arbitrator including: request monitoring means, responsive to a process request to begin or to cease accessing a device, for updating a list of monitored processes accordingly; and waiting means, responsive to termination of a monitored process, for determining any locked devices to which said process has access, and, responsive to no other monitored process having access to any of said locked devices, for releasing said client machine""s access to said devices and a method operable in a client arbitrator operable in a client arbitrator for a multi-processing operating system for monitoring and controlling a client machine""s access to one or more devices, said method comprising the steps of: responsive to a process request to begin or to cease accessing a device, updating a list of monitored processes accordingly; responsive to termination of a monitored process, determining any locked devices to which said process has access; and responsive to no other monitored process having access to any of said locked devices, releasing said client machine""s access to said devices.